金融系统中PBOC/EMV的TLV的算法实现（含C++/C#）
TLV即Tag-Length-Value，常在IC卡与POS终端设备中通过这样的一个应用通信协议进行数据交换。在金融系统以及认证中，PBOC以及EMV的认证规范文档上面也有对TLV做了一些说明，由于认证规范都是英文文档，所以有些人可能不易于理解。首先我先介绍下什么是TLV，TLV的用途是什么，以及如何实现它的打包解包算法。
金融系统中的TLV是BER-TLV编码的一个特例编码规范，而BER-TLV是ISO定义中的规范。在TLV的定义中，可以知道它包括三个域，分别为：标签域（Tag），长度域（Length），内容域（Value）。这里的长度域的值实际上就是内容域的长度。
其实，在BER编码的方式有两种情况，一种是确定长度的方式，一种是不确定长度的方式，而金融TLV选择了确定长度的方式，这样在设备之间的数据传输量上就可以减少。
Tag域说明：
先来看下TLV的Tag是如何编码的，先看下图：
这张图说明了Tag域第一个字节的编码格式。其中b8-b1代表1个字节中的8个位。
其中b8,b7代表数据的类别。根据2个位的组合，有四种类别：通用类别，应用类别，上下文语境类别，专用类别。这个主要用于在于终端设备交互的时候，确定数据处理的类型。
b6代表的是数据元结构，也就是说它是属于简单数据元结构，还是属于结构（复合）数据元结构。当b6为1的时候，就需要后续的字节进行扩展。也就是说复合的TLV中，value域里也包含一个或多个TLV，这个稍后接着介绍。
当b5-b1代表串行号，当5个位都为1时，需要将tag域扩展到下一个字节中，也就是Tag占2个字节；而当5个位都不全为1时，该Tag域就只占1个字节。
现在，看下b5-b1：11111的情况：
从图中我们看到BER-TLV编码中，当b8为1时，Tag还需要有后续字节，直到b8为0为止。从EMV文档中的说明，Tag最多只占用2个字节，所以这样就相对比较简单一些了。当b8为0时，该Tag域结束，总共就占用2个字节。
Length域说明：
在文档中没有图片叙述，我自绘一个：
当b8为0时，该字节的b7-b1作为value域的长度；当b8为1时，b7-b1作为后续字节的长度，也就是说，例如有这样一个值：10000011，代表后续还有3个字节作为value域的长度（本字节不算，本字节变为作为一个Length的索引）。3个字节代表value的长度，意味着什么呢，意味着内容的长度当需要很大的时候，字节的位数就会跟着越高，3个字节就代表最大可以有256*256*256的长度。
Value域说明：
也是分成两种情况考虑，就是前面说到的Tag分成两个数据元结构，一种是简单数据元结构，一种是复合数据元架构：
先来看看简单数据元结构：
Tag就是Tag,没有子标签Tag，基本结构就是T-L-V。
再看下符合数据元结构：
后面的Value说明：Primitive or constructed BER-TLV data object number，包含一个简单数据元结构或者也可以是一个符合数据元结构。这样可以看出，算法中必须要实现Tag的嵌套功能，递归算法不可少。
算法实现：
根据以上的说明现在来实现它的打包解包的算法（打包的目的是将一个从终端上发的请求数据——字节数组，构造成一系列的TLV结构实体；解包的目的刚好相反，就是将TLV结构实体解析成字节数组，然后通过IC卡发送到终端上）。
首先定义一个TLV结构实体：
// TLV结构体
struct TLVEntity {
unsigned char* Tag; //标记
unsigned char* Length; //数据长度
unsigned char* Value; //数据
unsigned int TagSize; //标记占用字节数
unsigned int LengthSize; //数据长度占用字节数
TLVEntity* Sub_TLVEntity; //子嵌套TLV实体
};
定义一个TLVPackage的打包类：
TLVPackage.h：
// TLV打包类
class TLVPackage
{
public:
TLVPackage();
virtual ~TLVPackage();
//构造TLV实体
static void Construct(unsigned char* buffer, unsigned int bufferLength, TLVEntity* tlvEntity, unsigned int& entityLength, unsigned int status=0);
//解析TLV字节数组
static void Parse(TLVEntity* tlvEntity, unsigned int entityLength, unsigned char* buffer, unsigned int& bufferLength);
};
具体方法实现：
// 构造TLV
void TLVPackage:: Construct(
unsigned char* buffer,
unsigned int bufferLength,
TLVEntity* tlvEntity,
unsigned int& entityLength,
unsigned int status
)
{
int currentTLVIndex = 0;
int currentIndex = 0;
int currentStatus = 'T'; //状态字符
unsigned long valueSize = 0;
while(currentIndex < bufferLength)
{
switch(currentStatus)
{
case 'T':
valueSize = 0;
//判断是否单一结构
if((status == 1 && buffer[currentIndex] & 0x20) != 0x20)
{
tlvEntity[currentTLVIndex].Sub_TLVEntity = NULL; //单一结构时将子Tag置空
//判断是否多字节Tag
if((buffer[currentIndex] & 0x1f) == 0x1f)
{
int endTagIndex = currentIndex;
while((buffer[++endTagIndex] & 0x80) == 0x80); //判断第二个字节的最高位是否为1
int tagSize = endTagIndex - currentIndex + 1; //计算Tag包含多少字节
tlvEntity[currentTLVIndex].Tag = new unsigned char[tagSize];
memcpy(tlvEntity[currentTLVIndex].Tag, buffer + currentIndex, tagSize);
tlvEntity[currentTLVIndex].Tag[tagSize] = 0;
tlvEntity[currentTLVIndex].TagSize = tagSize;
currentIndex += tagSize;
}
else
{
tlvEntity[currentTLVIndex].Tag = new unsigned char[1];
memcpy(tlvEntity[currentTLVIndex].Tag, buffer + currentIndex, 1);
tlvEntity[currentTLVIndex].Tag[1] = 0;
tlvEntity[currentTLVIndex].TagSize = 1;
currentIndex += 1;
}
}
else
{
//判断是否多字节Tag
if((buffer[currentIndex] & 0x1f) == 0x1f)
{
int endTagIndex = currentIndex;
while((buffer[++endTagIndex] & 0x80) == 0x80); //判断第二个字节的最高位是否为1
int tagSize = endTagIndex - currentIndex + 1; //计算Tag包含多少字节
tlvEntity[currentTLVIndex].Tag = new unsigned char[tagSize];
memcpy(tlvEntity[currentTLVIndex].Tag, buffer + currentIndex, tagSize);
tlvEntity[currentTLVIndex].Tag[tagSize] = 0;
tlvEntity[currentTLVIndex].TagSize = tagSize;
currentIndex += tagSize;
}
else
{
tlvEntity[currentTLVIndex].Tag = new unsigned char[1];
memcpy(tlvEntity[currentTLVIndex].Tag, buffer + currentIndex, 1);
tlvEntity[currentTLVIndex].Tag[1] = 0;
tlvEntity[currentTLVIndex].TagSize = 1;
currentIndex += 1;
}
//分析SubTag
int subLength = 0;
unsigned char* temp;
if((buffer[currentIndex] & 0x80) == 0x80)
{
for (int index = 0; index < 2; index++)
{
subLength += buffer[currentIndex + 1 + index] << (index * 8); //计算Length域的长度
}
temp = new unsigned char[subLength];
memcpy(temp, buffer + currentIndex + 3, subLength);
}
else
{
subLength = buffer[currentIndex];
temp = new unsigned char[subLength];
memcpy(temp, buffer + currentIndex + 1, subLength);
}
temp[subLength] = 0;
//memcpy(temp, buffer + currentIndex + 1, subLength);
unsigned int oLength;
tlvEntity[currentTLVIndex].Sub_TLVEntity = new TLVEntity[1];
Construct(temp, subLength, tlvEntity[currentTLVIndex].Sub_TLVEntity, oLength);
}
currentStatus = 'L';
break;
case 'L':
//判断长度字节的最高位是否为1，如果为1，则该字节为长度扩展字节，由下一个字节开始决定长度
if((buffer[currentIndex] & 0x80) != 0x80)
{
tlvEntity[currentTLVIndex].Length = new unsigned char[1];
memcpy(tlvEntity[currentTLVIndex].Length, buffer + currentIndex, 1);
tlvEntity[currentTLVIndex].Length[1] = 0;
tlvEntity[currentTLVIndex].LengthSize = 1;
valueSize = tlvEntity[currentTLVIndex].Length[0];
currentIndex += 1;
}
else
{
//为1的情况
unsigned int lengthSize = buffer[currentIndex] & 0x7f;
currentIndex += 1; //从下一个字节开始算Length域
for (int index = 0; index < lengthSize; index++)
{
valueSize += buffer[currentIndex + index] << (index * 8); //计算Length域的长度
}
tlvEntity[currentTLVIndex].Length = new unsigned char[lengthSize];
memcpy(tlvEntity[currentTLVIndex].Length, buffer + currentIndex, lengthSize);
tlvEntity[currentTLVIndex].Length[lengthSize] = 0;
tlvEntity[currentTLVIndex].LengthSize = lengthSize;
currentIndex += lengthSize;
}
currentStatus = 'V';
break;
case 'V':
tlvEntity[currentTLVIndex].Value = new unsigned char[valueSize];
memcpy(tlvEntity[currentTLVIndex].Value, buffer + currentIndex, valueSize);
tlvEntity[currentTLVIndex].Value[valueSize] = 0;
currentIndex += valueSize;
//进入下一个TLV构造循环
currentTLVIndex += 1;
currentStatus = 'T';
break;
default:
return;
}
}
entityLength = currentTLVIndex;
}
// 解析TLV
void TLVPackage::Parse(
TLVEntity* tlvEntity,
unsigned int entityLength,
unsigned char* buffer,
unsigned int& bufferLength
)
{
int currentIndex = 0;
int currentTLVIndex = 0;
unsigned long valueSize = 0;
while(currentTLVIndex < entityLength)
{
valueSize = 0;
TLVEntity entity = tlvEntity[currentTLVIndex];
memcpy(buffer + currentIndex, entity.Tag, entity.TagSize); //解析Tag
currentIndex += entity.TagSize;
for (int index = 0; index < entity.LengthSize; index++)
{
valueSize += entity.Length[index] << (index * 8); //计算Length域的长度
}
if(valueSize > 127)
{
buffer[currentIndex] = 0x80 | entity.LengthSize;
currentIndex += 1;
}
memcpy(buffer + currentIndex, entity.Length, entity.LengthSize); //解析Length
currentIndex += entity.LengthSize;
//判断是否包含子嵌套TLV
if(entity.Sub_TLVEntity == NULL)
{
memcpy(buffer + currentIndex, entity.Value, valueSize); //解析Value
currentIndex += valueSize;
}
else
{
unsigned int oLength;
Parse(entity.Sub_TLVEntity, 1, buffer + currentIndex, oLength); //解析子嵌套TLV
currentIndex += oLength;
}
currentTLVIndex++;
}
buffer[currentIndex] = 0;
bufferLength = currentIndex;
}
然后写测试程序：
// 上发测试数据
unsigned char requestBuf[] = {
0x9F, 0x1C, 0x12, 0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32, 0x30, 0x34, 0x30, 0x34,
0x32, 0x37, 0x31, 0x38, 0x9F, 0x62, 0x01, 0x01, 0x57, 0x12, 0x62, 0x22, 0x89, 0x00, 0x00, 0x02, 0x91,
0x01, 0xD0, 0x90, 0x32, 0x01, 0x02, 0x47, 0x17, 0x13, 0x00, 0x0F, 0x5F, 0x20, 0x0A, 0x48, 0x55, 0x47,
0x55, 0x4F, 0x20, 0x4D, 0x49, 0x4E, 0x47, 0x9F, 0x1F, 0x3C, 0x25, 0x39, 0x39, 0x36, 0x32, 0x32, 0x32,
0x38, 0x39, 0x30, 0x30, 0x30, 0x30, 0x30, 0x32, 0x39, 0x31, 0x30, 0x31, 0x5E, 0x47, 0x55, 0x4F, 0x20,
0x4D, 0x49, 0x4E, 0x47, 0x2F, 0x48, 0x55, 0x5E, 0x30, 0x39, 0x30, 0x33, 0x32, 0x30, 0x31, 0x30, 0x32,
0x34, 0x37, 0x31, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x32, 0x38, 0x39, 0x30,
0x30, 0x3F
};
TLVEntity tlvEntity[TLV_MAX_LENGTH];
unsigned int tlv_count;
//构造TLV
TLVPackage::Construct(requestBuf, sizeof(requestBuf), tlvEntity, tlv_count);
unsigned char parseBuf[1024];
unsigned int buf_count;
//解析TLV
TLVPackage::Parse(tlvEntity, tlv_count, parseBuf, buf_count);
if(strncmp((char*)parseBuf, (char*)requestBuf, sizeof(requestBuf)) == 0)
{
AfxMessageBox("TRUE");
}
else
{
AfxMessageBox("FALSE");
}
最后测试结果中，可以得到最后将弹出“TRUE”的对话框。证明构造TLV得到的TLVEntity，再对这个实体进行解析，可以的到解析后的字节数组，最后通过strncmp的方法比较判断，是否原始字节数组和解析后的字节数组是否一致。
另外，为了方便C#程序员的使用，我对该C++程序重新改写了一下，得出的结果也是一样的。
TLVEntity.cs
///
/// TLV实体
///
public class TLVEntity
{
///
/// 标记
///
public byte[] Tag { get; set; }
///
/// 数据长度
///
public byte[] Length { get; set; }
///
/// 数据
///
public byte[] Value { get; set; }
///
/// 标记占用字节数
///
public int TagSize { get; set; }
///
/// 数据长度占用字节数
///
public int LengthSize { get; set; }
///
/// 子嵌套TLV实体
///
public TLVEntity Sub_TLVEntity { get; set; }
}
以及TLVPackage.cs
///
/// TLV打包类
///
public class TLVPackage
{
///
/// 构造TLV
///
///
public static List Construct(byte[] buffer)
{
List list = new List();
int currentTLVIndex = 0;
int currentIndex = 0;
int currentStatus = 'T'; //状态字符
int valueSize = 0;
TLVEntity tlvEntity = null;
while (currentIndex < buffer.Length)
{
switch (currentStatus)
{
case 'T':
tlvEntity = new TLVEntity();
valueSize = 0;
//判断是否单一结构
if ((buffer[currentIndex] & 0x20) != 0x20)
{
tlvEntity.Sub_TLVEntity = null; //单一结构时将子Tag置空【】
//判断是否多字节Tag
if ((buffer[currentIndex] & 0x1f) == 0x1f)
{
int endTagIndex = currentIndex;
while ((buffer[++endTagIndex] & 0x80) == 0x80) ; //判断第二个字节的最高位是否为1
int tagSize = endTagIndex - currentIndex + 1; //计算Tag包含多少字节
tlvEntity.Tag = new byte[tagSize];
Array.Copy(buffer, currentIndex, tlvEntity.Tag, 0, tagSize);
tlvEntity.TagSize = tagSize;
currentIndex += tagSize;
}
else
{
tlvEntity.Tag = new byte[1];
Array.Copy(buffer, currentIndex, tlvEntity.Tag, 0, 1);
tlvEntity.TagSize = 1;
currentIndex += 1;
}
}
else
{
//判断是否多字节Tag
if ((buffer[currentIndex] & 0x1f) == 0x1f)
{
int endTagIndex = currentIndex;
while ((buffer[++endTagIndex] & 0x80) == 0x80) ; //判断第二个字节的最高位是否为1
int tagSize = endTagIndex - currentIndex + 1; //计算Tag包含多少字节
tlvEntity.Tag = new byte[tagSize];
Array.Copy(buffer, currentIndex, tlvEntity.Tag, 0, tagSize);
tlvEntity.TagSize = tagSize;
currentIndex += tagSize;
}
else
{
tlvEntity.Tag = new byte[1];
Array.Copy(buffer, currentIndex, tlvEntity.Tag, 0, 1);
tlvEntity.TagSize = 1;
currentIndex += 1;
}
//分析SubTag
int subLength = 0;
byte[] temp;
if ((buffer[currentIndex] & 0x80) == 0x80)
{
for (int index = 0; index < 2; index++)
{
subLength += buffer[currentIndex + 1 + index] << (index * 8); //计算Length域的长度
}
temp = new byte[subLength];
Array.Copy(buffer, currentIndex + 3, temp, 0, subLength);
}
else
{
subLength = buffer[currentIndex];
temp = new byte[subLength];
Array.Copy(buffer, currentIndex + 1, temp, 0, subLength);
}
int oLength;
tlvEntity.Sub_TLVEntity = new TLVEntity();
List tempList = Construct(temp);
tlvEntity.Sub_TLVEntity = tempList[0];
}
currentStatus = 'L';
break;
case 'L':
//判断长度字节的最高位是否为1，如果为1，则该字节为长度扩展字节，由下一个字节开始决定长度
if ((buffer[currentIndex] & 0x80) != 0x80)
{
tlvEntity.Length = new byte[1];
Array.Copy(buffer, currentIndex, tlvEntity.Length, 0, 1);
tlvEntity.LengthSize = 1;
valueSize = tlvEntity.Length[0];
currentIndex += 1;
}
else
{
//为1的情况
int lengthSize = buffer[currentIndex] & 0x7f;
currentIndex += 1; //从下一个字节开始算Length域
for (int index = 0; index < lengthSize; index++)
{
valueSize += buffer[currentIndex + index] << (index * 8); //计算Length域的长度
}
tlvEntity.Length = new byte[lengthSize];
Array.Copy(buffer, currentIndex, tlvEntity.Length, 0, lengthSize);
tlvEntity.LengthSize = lengthSize;
currentIndex += lengthSize;
}
currentStatus = 'V';
break;
case 'V':
tlvEntity.Value = new byte[valueSize];
Array.Copy(buffer, currentIndex, tlvEntity.Value, 0, valueSize);
currentIndex += valueSize;
//进入下一个TLV构造循环
list.Add(tlvEntity);
currentStatus = 'T';
break;
default:
return new List();
}
}
return list;
}
///
/// 解析TLV
///
///
///
public static byte[] Parse(List list)
{
byte[] buffer = new byte[4096];
int currentIndex = 0;
int currentTLVIndex = 0;
int valueSize = 0;
while (currentTLVIndex < list.Count())
{
valueSize = 0;
TLVEntity entity = list[currentTLVIndex];
Array.Copy(entity.Tag, 0, buffer, currentIndex, entity.TagSize); //解析Tag
currentIndex += entity.TagSize;
for (int index = 0; index < entity.LengthSize; index++)
{
valueSize += entity.Length[index] << (index * 8); //计算Length域的长度
}
if (valueSize > 127)
{
buffer[currentIndex] = Convert.ToByte(0x80 | entity.LengthSize);
currentIndex += 1;
}
Array.Copy(entity.Length, 0, buffer, currentIndex, entity.LengthSize); //解析Length
currentIndex += entity.LengthSize;
//判断是否包含子嵌套TLV
if (entity.Sub_TLVEntity == null)
{
Array.Copy(entity.Value, 0, buffer, currentIndex, valueSize); //解析Value
currentIndex += valueSize;
}
else
{
byte[] tempBuffer = Parse(new List { entity.Sub_TLVEntity });
Array.Copy(tempBuffer, 0, buffer, currentIndex, tempBuffer.Length); //解析子嵌套TLV
currentIndex += tempBuffer.Length;
}
currentTLVIndex++;
}
byte[] resultBuffer = new byte[currentIndex];
Array.Copy(buffer, 0, resultBuffer, 0, currentIndex);
return resultBuffer;
}
}
接着，写测试程序：
static byte[] requestBuffer =
{
0x9F, 0x1C, 0x82, 0x2C, 0x01,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,0x33, 0x33, 0x30, 0x32, 0x32, 0x37, 0x31, 0x39, 0x36, 0x32,
0x71, 0x07, 0x9f, 0x19, 0x04, 0x11, 0x22, 0x33, 0x44
};
static void Main(string[] args)
{
Console.WriteLine("待组装的数据包：");
requestBuffer.ToList().ForEach(o => { Console.Write("{0},", "0x" + o.ToString("X")); });
Console.WriteLine("\r\n\r\n开始构造TLV");
//构造TLV
List list = TLVPackage.Construct(requestBuffer);
Console.WriteLine("\r\n构造结束!");
Console.WriteLine("\r\n开始解析TLV");
//解析TLV
byte[] responseBuffer = TLVPackage.Parse(list);
Console.WriteLine("\r\n解析结束!");
Console.WriteLine("\r\n解析结果：");
if (ByteEquals(requestBuffer, responseBuffer))
{
Console.WriteLine("Equal!");
}
else
{
Console.WriteLine("Not Equal!");
}
Console.ReadKey();
}
运行结果：
总结
TLV在数据通信方面，其实运用得很广泛，在应用层数据通信中，如HTTP协议，HTML，XML语言本身定义了一些标签（Body，Head，Script）对数据串行化，接收方再根据标签解析原始数据，通过浏览器展现出来。因此本质上也是属于TLV协议的设计模式。甚至在传输层的TCP，UDP协议，你完全可以通过TLV实现自定义的应用协议。